MqttAndroidClient.publish()方法时空指针。

问题描述：安卓mqtt发送一条消息，发送之前检测网络，发现网络突然断了，又突然连上了，此时发送消息时，报空指针 mClient不设置为空的话 ，始终不为null

相关代码：

public void publish(String topic, String message) {
    try {
        InsideApplication.getSharedPreferences().getString(Const.ROOM_ID, "");
        String roomTopic = topic;
        if (!isNetworkConnected(InsideApplication.getApplication())) {
            LogUtils.d(TAG, "publish()--没有网");
            //在这里尝试过注销这mClient广播接收器 设置成null，
            //这个网络断开和连接非常快设置了睡眠 也无用
        }
if (mClient == null) {
            mClient = new MqttAndroidClient(InsideApplication.getApplication(), mUri,       DeviceUuidFactory.getLocalSerialHex());
            mClient.setCallback(this);
            //连接
        }
        mClient.publish(
                roomTopic, 
                message.getBytes(), 
                MQTTConfig.QOS, 
                false, 
                null, 
                new ActionListener(
                        mContext, 
                        Action.PUBLISH, 
                        this));
    } catch (MqttSecurityException e) {
    } catch (MqttException e) {
    }

报错信息：

Caused by: java.lang.NullPointerException

at org.eclipse.paho.android.service.MqttAndroidClient.publish(MqttAndroidClient.java:715)
at com.insideroom.mqtt.MQTTConnect.publish(MQTTConnect.java:112)
at com.insideroom.base.InsideApplication.publish(InsideApplication.java:93)
at com.insideroom.activity.VoiceNameActivity.pushNET(VoiceNameActivity.java:224)
at com.insideroom.activity.VoiceNameActivity.onCreate(VoiceNameActivity.java:110)
at android.app.Activity.performCreate(Activity.java:5131)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1090)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
... 11 more